Lacrimal fluid (commonly called "tears") is normally supplied continuously to the human eye from the lacrimal gland. Excess fluid drains through canaliculi or small passageways commencing adjacent the inner corner of the eye. Fluid collects in the lacrimal sac before draining via the nasolacrimal duct into the inferior nasal meatus. For the purposes of this disclosure, the passages forming the drainage system will be referred to collectively as the lacrimal ducts.
Some medical conditions can arise where lacrimal ducts become blocked so that fluid can no longer flow to the nasal meatus. These conditions include congenital anomalies, accidents, inflammation and advanced aging, as well as other physiological conditions. The result is that the eye is continually brimming over with fluid causing much personal discomfort to the patient.
Several devices have been proposed for correcting blocked lacrimal ducts. One is described in U.S. Pat. No. 2,154,968 to Alkio which issued in 1939. This patent teaches a structure consisting of several parts including a rigid tubular probe which contains a very flexible fine wire. The end of the wire is enlarged to retain the wire in the tube and the probe is inserted through the lacrimal duct until it projects into the inferior meatus of the nose. Then, by withdrawing the tube partially, the wire can be withdrawn through the meatus using a tool which traps the enlarged end of the wire. The flexibility of the wire permits the wire to bend with minimal resistance where the nasolacrimal duct meets the inferior meatus. A spiral canula is then slipped up the wire and into the lacrimal duct so that the wire can subsequently be withdrawn upwardly leaving the spiral canula in place.
A second structure was proposed by Dr. P. Guibor who presented a new device at the 79th Annual Meeting of the American Academy of Oxology and Otolaryngology which was held in Dallas, Tex. on Oct. 6-10 of 1974. Dr. Guibor described a structure consisting of a pair of quite stiff stainless steel probes that attach one to each end of a length of Silastic tubing (trade mark of Dow Corning). The tubing is attached to end portions of the probe which are of tempered stainless steel with sufficient stiffness to ensure that the arched shape of the probes tends to maintain its shape in use. In this respect, Dr. Guibor's structure has a similarity to the Alkio structure because in both structures the probe is quite stiff and is designed to retain its shape as it is pushed downwardly into the lacrimal duct. This stiffness was apparently considered to be necessary in such devices and is in marked contrast with a further prior art structure shown in U.S. Pat. No. 4,380,239 which issued on Apr. 19, 1983 to Dr. John Crawford et al.
Dr. Crawford's structure provided a probe set consisting of a light wire which can be readily deflected through an angle of at least 90.degree. to permit the probe to pass from the nasolacrimal duct to the inferior meatus. The probe has an enlarged end portion which is rounded to limit the possibility of damage to tissue when the probe is inserted, and a very flexible tube of minimal rigidity having a first end attached to the probe remote from the end portion and having an outside diameter comparable to that of the end portion. In use the probe can be inserted and used to draw the tube into the lacrimal duct. The enlarged end is also used to draw the device through the lacrimal duct by using the hook shown in the Crawford patent.
While Dr. Crawford's device has achieved significant commercial success, it is an object of the present invention to provide an improved structure, and more particularly an improved structure using the principles taught in Crawford et al U.S. Pat. No. 4,380,239.
The structure taught by Dr. Crawford et al also includes an enlargement where the probe is attached to the tubing. The enlargement has a diameter matching that of the tubing so that the tubing can be pushed onto the wire and into engagement with the enlargement. As a result, as the wire is drawn through the lacrimal duct, the enlargement protects the end of the tube and prevents a load being applied to the tube tending to separate the tube from the probe.
Such an arrangement has been proven to be commercially successful but the difficulty of preparing a probe of this kind with the enlargement positioned on the probe, has increased the cost of manufacture.
A further disadvantage of the structure taught by Dr. Crawford is the stress concentration that can be developed where the tube meets the probe. The tube is extremely flexible and can be pulled at right angles to the direction of the probe without significantly bending the probe. This can result in tearing the tube due to the build up in stress in the tube where it meets the probe.
Such disadvantages of the prior art are addressed in the present invention.